Claude says the following;
Subject: Re: bash while loop syntax for weewx backup script
Hi,
I think I spotted the issue. Your while condition is:
while [ systemctl -q is-active weewx ];
The problem is that [ ... ] is the "test" command - it doesn't actually run
systemctl at all. It just checks whether the string "systemctl -q is-active
weewx" is non-empty, which is always true, so the loop never ends based on
weewx's real state (it just happens to work when weewx stops quickly, since the
loop body still runs and eventually you get lucky with timing).
The fix is to drop the [ ] brackets entirely and use the command itself as the
condition. In bash, while just checks the exit status of whatever command you
give it - it doesn't need [ ] at all unless you're testing a string, number, or
file:
while systemctl -q is-active weewx;
do
sleep 1
echo $(date): Weewx is still stopping >> /var/log/weewx-backup.log
done
systemctl -q is-active weewx exits 0 (true) while the service is active, and
non-zero once it's fully stopped - which is exactly what you want the loop to
check.
General rule of thumb: use while [ condition ] for string/number/file tests,
and while some_command when you want to "loop while this command succeeds."
Your instinct not to copy the DB mid-write is exactly right, and this fix makes
that work as intended.
One more suggestion: it's worth adding a timeout guard in case weewx ever hangs
on stop, so the script can't wait forever. Here's the full script with that
added:
#!/bin/bash
#
# Stop weewx service
echo $(date): Weewx is stopping >> /var/log/weewx-backup.log
systemctl stop weewx
#
# Check service has stopped (with timeout)
timeout=30
count=0
while systemctl -q is-active weewx;
do
if [ $count -ge $timeout ]; then
echo $(date): Weewx did not stop after ${timeout}s - aborting
backup >> /var/log/weewx-backup.log
systemctl start weewx
exit 1
fi
sleep 1
count=$((count + 1))
echo $(date): Weewx is still stopping >> /var/log/weewx-backup.log
done
echo $(date): Weewx has stopped >> /var/log/weewx-backup.log
#
# Copy files to backup folder
echo $(date): Backup is starting >> /var/log/weewx-backup.log
tar -czvf /mnt/backup/weewx-conf.tar.gz /etc/weewx
tar -czvf /mnt/backup/weewx-db.tar.gz /var/lib/weewx/weewx.sdb
echo $(date): Backup is complete >> /var/log/weewx-backup.log
#
# Start weewx service
systemctl start weewx
echo $(date): Weewx is starting >> /var/log/weewx-backup.log
With the timeout added, if weewx ever fails to stop within 30 seconds, the
script restarts weewx, logs the failure, and exits before touching the backup
files - so a hung stop can't leave weewx down or risk copying a database
mid-write.
Hope that helps!
________________________________
From: [email protected] <[email protected]> on behalf of
David Schulz <[email protected]>
Sent: Monday, September 21, 2026 7:22 PM
To: weewx-user <[email protected]>
Subject: [weewx-user] Assistance with While condition for backup script
Hi
I'm attempting to write my first bash script to backup weewx. I'm struggling
with the syntax of a condition for a while loop that checks if weewx has
stopped or is still stopping.
I don't really understand the syntax of the example conditions I can find for
various tutorials on using while to create a loop. I cannot find anywhere an
exact example of using 'systemctl is-active' as the condition for a while loop.
Appreciate any feedback from people more learned than I.
TIA
Here's what I have at the moment. If I run this script when I know weewx won't
be writing to the database, the commands to zip the files into the backup
directory all work OK.
I don't think I want to be copying the database file in the middle of a write.
So I have a separate script with the backup section removed just trying to test
the stopping, check has stopped and start parts of the script. I've been
unsuccessfully futzing around with different condition syntax and actively
trying to run it when weewx is active and the stop command will take a while to
execute while the weewx main loop completes. But TBH I'm just wandering about
in the dark.
```
#!/bin/bash
#
# Stop weewx service
echo $(date): Weewx is stopping >> /var/log/weewx-backup.log
systemctl stop weewx
#
# Check service has stopped
while [ systemctl -q is-active weewx ];
do
sleep 1
echo $(date): Weewx is still stopping >> /var/log/weewx-backup.log
done
echo $(date): Weewx has stopped >> /var/log/weewx-backup.log
#
# Copy files to backup folder
echo $(date): Backup is starting >> /var/log/weewx-backup.log
tar -czvf /mnt/backup/weewx-conf.tar.gz /etc/weewx
tar -czvf /mnt/backup/weewx-db.tar.gz /var/lib/weewx/weewx.sdb
echo $(date): Backup is complete >> /var/log/weewx-backup.log
#
# Start weewx service
systemctl start weewx
echo $(date): Weewx is starting >> /var/log/weewx-backup.log
```
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